John Morton, the director of the U.S. Immigration and Customs Enforcement agency, will step down at the end of July to go to the private sector. / Alex Wong Getty Images

by Alan Gomez, USA TODAY

by Alan Gomez, USA TODAY

WASHINGTON -- President Obama's immigration enforcement director announced his resignation Monday, ending a four-year tenure that saw a dramatic shift in how the federal government pursues and deports unauthorized immigrants.

In an internal letter to colleagues on Monday, Immigration and Customs Enforcement Director John Morton announced he would depart the agency by the end of July and start working for a private company.

He will be moving to Capital One, the Fortune 500 financial services company, and be based in its McLean, Va., headquarters as head of the company's compliance office, the company said in a statement.

"He is a skilled leader with great judgment and a proven ability to drive results in a dynamic organization," Capital One spokeswoman Tatiana Stead said. "Compliance is a high priority for our company, and we couldn't be more pleased that he will be joining our team."

In his letter, Morton thanked his colleagues for their work and said it was simply time for his 20-year government career, which included years at the Justice Department, to come to an end.

"I am extremely proud of what we have accomplished together during that time and look with awe on the incredible progress ICE has made as an agency," Morton wrote. "ICE has truly come of age and become an innovative, leading force in federal law enforcement."

Morton leaves the agency with high praise from officials in the Obama administration, but a stream of complaints from immigration advocates and hard-liners alike who feel he either went too far, or did too little, in targeting unauthorized immigrants for deportation.

"I am deeply grateful for Director Morton's contributions to (the Department of Homeland Security), ICE and our nation and I wish him all the best in his coming endeavors," Homeland Security Secretary Janet Napolitano said in a statement. "John will be missed."

Morton may best be remembered for a policy plan he authored in 2011 -- known in immigration circles as the "Morton Memo" -- which outlined a new strategy for determining whom the agency should deport.

In the memo, Morton explained that ICE has a limited amount of money and resources it can dedicate to deporting any of the 11 million unauthorized immigrants living in the country. So he ordered his agents to use "prosecutorial discretion" to focus deportation proceedings on certain groups of unauthorized immigrants, including those who pose a national security threat, who have extensive criminal backgrounds and recent border-crossers.

That strategy was dubbed "amnesty by any means" by the Center for Immigration Studies, a group that advocates for lower levels of immigration, and had already earned him a vote of "no confidence" from the National ICE Council, the biggest labor union for ICE employees.

"He was the architect of the administration's non-enforcement policy," said Ira Mehlman of the Federation for American Immigration Reform. "He was toeing the administration's line rather than allowing them to do the jobs they were sworn to do."

Despite those claims, the Obama administration continued setting a record each year for the number of people it deports -- more than 400,000 in 2012. During Morton's tenure, the percentage of people deported who were convicted criminals rose from 38% in 2009 to 55% in 2012.

Homeland Security officials point to those numbers to show how ICE has been able to spend its limited time on people who are criminals and serious threats to the country. But the sheer volume of people deported has led immigration advocates to label Obama as the "deporter in chief" and single out Morton for carrying out those deportations.

"Under his leadership, ICE further fractured an already broken immigration system, it did tremendous damage to civil rights, and it served as a 'force multiplier' for the unjust status quo," Chris Newman, legal director for the National Day Laborer Organizing Network, said in a statement. "While we celebrate the removal of Morton, the deportation machine he helped build remains in place."